1. Field of the Invention
The present invention relates generally to windmills, and more specifically, to windmills suspended from non-rigid support structures.
2. DESCRIPTION OF THE RELATED ART
With ongoing depletion of natural resources, alternative sources of energy need to be developed. While solar and wind power have been explored extensively, problems persist which render both these alternative sources of energy impractical.
One of the problems associated with wind power is that windmills generally require large, permanently installed, rigid support structures or towers to support a rotor at a sufficiently high elevation to place the rotor in a higher velocity air stream. Once installed, a windmill is dependent upon the wind conditions prevalent at its permanent location. Also, rigid support structures are generally complex and expensive to build.
As an alternative to rigid structures, it has been proposed to suspend rotors or "windmills" from balloons which are capable of placing the rotor at much higher elevations. In U.S. Pat. No. 4,073,516, gimble-mounted circular rotors are suspended from a balloon which is tethered to the ground by one or more stays.
U.S. Pat. No. 4,486,669 describes another balloon-suspended windmill which is tethered to the ground. The generators are mounted in a box-like kite enclosure. The rotors of the wind generators or windmills are raised and lowered to achieve maximum electrical output by means of the gas balloon.
U.S. Pat. No. 4,470,563 describes another windmill suspended from a balloon. Instead of producing electric current and feeding the current to the ground by an electrical cable, the rotors simply turn belts which run to the ground and turn a ground-mounted generator.
Balloon-suspended windmills of the type described in the above U.S. patents have numerous drawbacks. For instance, the balloons must be replenished with gas in order to maintain the position of the rotor. Also, the balloons are susceptible to high winds and lightning. Should the balloons suffer a leak, the rotor and generator associated therewith would be destroyed by falling to the ground. Another problem associated with balloon-suspended windmills is that, even with moderate winds, the position of the rotor will be difficult to maintain.
U.S. Pat. No. 4,217,501 describes a windmill mounting system in which twin towers are used to support a plurality of horizontal cables therebetween. A mast has one end connected to one of the horizontal cables and an opposite end connected to an adjacent horizontal cable and is thus disposed in a vertical orientation. A rotor assembly is connected to the mast, which is freely rotatable at its opposite ends.
In the aforementioned U.S. Pat. No. 4,217,501, a true "suspension" is not achieved since the mast is connected at its opposite ends to two horizontal cables. The requirement of a rigid mast reduces the practical uses of the windmill apparatus. The mast described in U.S. Pat. No. 4,217,501 is required to make the rotor assembly statically and dynamically stable.